Individual fuel cells have been used both experimentally and commercially in various configurations to power various electrical loads. In the main, the applications have relied on a single fuel cell, or fuel cell power plant, to supply electrical power to one or more loads at the site. While such sites may be mobile, as in the powering of the electric drive motor of a vehicle, in the main they are large and stationary. These applications have typically been individual commercial installations or buildings, perhaps involving computers or similar electronic data processing equipment or medical equipment requiring a reliable source of power.
To operate such fuel cell power plants, there are normally associated various controls for the direct control of the fuel cell itself and its production of DC electrical power, as well as additional controls for convening the DC power to AC power, for connecting and disconnecting power with the loads, etc. In some instances, the fuel cell power plant is connected to the loads in parallel with the normal electric utility grid, and may act in lieu of, or in addition to, the grid to supply power to the loads. In other instances, there may be multiple fuel cell power plants at a site, collectively connected to the loads in parallel with the utility grid. However, even in such configuration, the control of the fuel cells has typically been on an individual basis, with little or no provision for an integrated control arrangement to optimize the use of multiple fuel cell power plants interconnected with the utility grid and the loads.
When one or more fuel cell power plants are connected to the utility grid as well as the loads, they are said to be in a grid connected (GIC) configuration or mode. Alternatively, when those fuel cell power plants are connected only to the loads, they are said to be in grid independent (G/I) mode. In the G/I mode, the fuel cell power plants typically follow the load and apportion the load among the power plants. The transition from one such mode to the other, and the control of multiple fuel cell power plants relative to the loads present additional control complexities that have impeded the efficient and economic utilization of multiple fuel cell power plants as distributed resources in electric utility grids.
Accordingly, it is an object of the invention to provide a power system having a control arrangement for the efficient and economic utilization of multiple fuel cell  power plants, e.g., fuel cells, at a site as a distributed resource in a utility grid.
It is a further object of the invention to provide a control arrangement to optimize the interrelationship between multiple fuel cell power plants and multiple loads at a site in order to enhance utilization of the plants as a distributed resource in a utility grid.
It is a still further object to provide a control arrangement for a multiple fuel cell power plant generation system at a site that coordinates operation of the fuel cell power plants in an integrated, or unified, manner in both the G/C and the G/I modes of operation.